The present invention relates to a workpiece carrier for conveying a workpiece to be painted, in particular, a vehicle body through at least one electrophoretic dip paint bath and by means of at least one conveyor device which follows the electrophoretic dip paint bath, the carrier comprising at least one electrical contacting device for passing a coating current into the workpiece when the workpiece is conveyed through the electrophoretic dip paint bath and at least one contact surface, at which the workpiece carrier comes into contact with the conveyor device following the electrophoretic dip paint bath.
Workpiece carriers of this type are known from the state of the art and can be designed, in particular, as skid frames.
A “skid frame” is to be understood as a workpiece carrier which has at least two skid runners which are aligned along the direction of conveyance of the workpiece and spaced from one another transversely to the direction of conveyance of the workpiece, wherein each skid runner has a contact surface for supporting the skid frame on the conveyor device.
In this respect, the skid runners of the skid frame can be mounted directly on the workpiece so that the workpiece itself undertakes the connection of the skid runners with one another. The term “skid frame”, as used in this description and in the attached claims, also comprises a configuration, with which the skid runners are mounted directly on the workpiece without being connected to one another by crossbars.
If skid conveyor technology is used for conveying vehicle bodies through the pretreatment baths and the electrophoretic dip paint bath of a paint plant, each vehicle body will be placed on a dip skid frame when entering the pretreatment area or already as a body-in-white and then passes through the pretreatment baths, the electrophoretic dip paint bath and also the drier following the electrophoretic dip paint bath on this skid frame. Subsequently, the vehicle body is changed to another skid frame, on which the vehicle body is conveyed through a subsequent spray paint section of the paint plant.
The dip skid frame, on which the vehicle body is conveyed through the electrophoretic dip paint bath, is normally manufactured from black normal steel. When these skid frames are brought into operation they travel through the pretreatment baths and the electrophoretic dip paint bath as well as the dip paint drier. In this respect, the skid frame is coated with dip paint. In the dip paint drier, this paint coating will be hardened and then serves as a protection against corrosion for the skid frame.
This paint protection layer is maintained on the skid frame, apart from the coating of the contact surfaces on the skid runners and apart from places on the locking mechanisms between the skid frame and the vehicle body. The paint coating on the skid runners will be rubbed off by the conveyor technology arranged between the exit from the electrophoretic dip paint plant and the entry into the drier at the places where contact is made between the conveyor technology and the skid frame. The holding time in this section is approximately 15 minutes in order to allow the paint sufficient time to run out of slits in the vehicle body.
The sticky paint which is rubbed off the skid runners in this conveyor section and is not yet hardened will be distributed in this way in the entire conveyor technology connecting the electrophoretic dip paint bath to the drier and must be cleaned off manually during operational stoppages of the paint plant, for example, at weekends.
This soiling with rubbed-off paint is even to be found in the cooling zone of the drier after the paint on the vehicle body has successfully hardened. Whereas the paint on the surface of the vehicle body remains for a sufficient time at the hardening temperature, the underside of the skid runners is, on the one hand, not subjected to the flow of hot air in the dip paint drier and cannot, on the other hand, be heated up quickly enough, on account of the large mass of the skid runners, and so the paint on the underside of the skid runners leaves the drier uncured.
The object underlying the present invention is to create a workpiece carrier of the type specified at the outset, with which dip paint is prevented from rubbing off in the conveyor device following the electrophoretic dip paint bath.